Body fat calculator — US Navy method

Measure neck and waist with a tape (hips too if you're female) — estimate body fat % in a few minutes.

This is a tape estimate, not a lab result — usually within about ±3–4 percentage points. Don't treat it as a diagnosis; ask a doctor or dietitian if you're unsure.

Input data

Result

Fill in the measurements and click Calculate.

How results are calculated

US Navy method: enter girths and height in cm (metric header); the formula converts to inches internally.

Men: 86.010×log₁₀(waist−neck) − 70.041×log₁₀(height) + 36.76.

Women: 163.205×log₁₀(waist+hip−neck) − 97.684×log₁₀(height) − 78.387.

Optional weight (kg): % BF → fat and lean mass in kg.

How to use the calculator

  1. Choose your sex — the form will adjust the measurement fields.
  2. Enter your height and neck circumference.
  3. Enter your waist circumference (men: at navel; women: narrowest point) — women also enter hip circumference.
  4. Optionally enter weight to see fat mass and lean mass.
  5. Click Calculate to see your result and category.

Usage examples

Example 1 — Man

  • Height: 180 cm, neck: 38 cm
  • Waist: 90 cm, weight: 85 kg

BF ≈ 19.9% — average

A typical result for a moderately fit man.

Example 2 — Woman

  • Height: 165 cm, neck: 32 cm
  • Waist: 65 cm, hip: 95 cm

BF ≈ 22.4% — fitness

A result within the typical range for active women.

Example 3 — Man

  • Height: 175 cm, neck: 40 cm
  • Waist: 100 cm, weight: 98 kg

BF ≈ 26.1% — obese range

A larger waist relative to the neck raises the estimated body fat %.

FAQ

Where does the tape % come from?

The US Navy method plugs neck, waist (and hips for women) plus height into a log formula. You get a quick BF% without hydrostatic weighing or DEXA.

How do I measure so I don't wreck the result?

Tape snug, not digging in. Waist at the narrowest point or navel height; neck under the larynx; hips at the widest point. Measure the same way every time.

How accurate is it?

For most people usually ±3–4 points vs lab. Fine for tracking trends, not medical precision.

Why is the form different for women?

Navy's female formula also uses hip circumference — that's the extra field.

What do the result categories mean?

Rough fitness bands (essential / fitness / average, etc.). Not a medical diagnosis — compare your own measurements over time first.

Why enter weight if the formula doesn't use it?

For context and linked calculators (BMI, protein). Navy BF% itself comes from circumferences and height.

Can I compare measurements across days?

Yes, if you measure at a similar time with the same technique. Morning fasted is usually most repeatable.

What about very lean or very heavy people?

At the extremes, tape estimates get shakier. Treat the number cautiously and confirm another way if you need to.

Related calculators

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Body mass index and category.

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BMR — basal metabolic rate

Resting energy use.

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Protein requirement

Grams of protein per day by goal.

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